github.com/mdempsky/go@v0.0.0-20151201204031-5dd372bd1e70/src/unicode/utf8/utf8.go (about)

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package utf8 implements functions and constants to support text encoded in
     6  // UTF-8. It includes functions to translate between runes and UTF-8 byte sequences.
     7  package utf8
     8  
     9  // The conditions RuneError==unicode.ReplacementChar and
    10  // MaxRune==unicode.MaxRune are verified in the tests.
    11  // Defining them locally avoids this package depending on package unicode.
    12  
    13  // Numbers fundamental to the encoding.
    14  const (
    15  	RuneError = '\uFFFD'     // the "error" Rune or "Unicode replacement character"
    16  	RuneSelf  = 0x80         // characters below Runeself are represented as themselves in a single byte.
    17  	MaxRune   = '\U0010FFFF' // Maximum valid Unicode code point.
    18  	UTFMax    = 4            // maximum number of bytes of a UTF-8 encoded Unicode character.
    19  )
    20  
    21  // Code points in the surrogate range are not valid for UTF-8.
    22  const (
    23  	surrogateMin = 0xD800
    24  	surrogateMax = 0xDFFF
    25  )
    26  
    27  const (
    28  	t1 = 0x00 // 0000 0000
    29  	tx = 0x80 // 1000 0000
    30  	t2 = 0xC0 // 1100 0000
    31  	t3 = 0xE0 // 1110 0000
    32  	t4 = 0xF0 // 1111 0000
    33  	t5 = 0xF8 // 1111 1000
    34  
    35  	maskx = 0x3F // 0011 1111
    36  	mask2 = 0x1F // 0001 1111
    37  	mask3 = 0x0F // 0000 1111
    38  	mask4 = 0x07 // 0000 0111
    39  
    40  	rune1Max = 1<<7 - 1
    41  	rune2Max = 1<<11 - 1
    42  	rune3Max = 1<<16 - 1
    43  
    44  	// The default lowest and highest continuation byte.
    45  	locb = 0x80 // 1000 0000
    46  	hicb = 0xBF // 1011 1111
    47  
    48  	// These names of these constants are chosen to give nice alignment in the
    49  	// table below. The first nibble is an index into acceptRanges or F for
    50  	// special one-byte cases. The second nibble is the Rune length or the
    51  	// Status for the special one-byte case.
    52  	xx = 0xF1 // invalid: size 1
    53  	as = 0xF0 // ASCII: size 1
    54  	s1 = 0x02 // accept 0, size 2
    55  	s2 = 0x13 // accept 1, size 3
    56  	s3 = 0x03 // accept 0, size 3
    57  	s4 = 0x23 // accept 2, size 3
    58  	s5 = 0x34 // accept 3, size 4
    59  	s6 = 0x04 // accept 0, size 4
    60  	s7 = 0x44 // accept 4, size 4
    61  )
    62  
    63  // first is information about the first byte in a UTF-8 sequence.
    64  var first = [256]uint8{
    65  	//   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
    66  	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x00-0x0F
    67  	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x10-0x1F
    68  	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x20-0x2F
    69  	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x30-0x3F
    70  	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x40-0x4F
    71  	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x50-0x5F
    72  	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x60-0x6F
    73  	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x70-0x7F
    74  	//   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
    75  	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x80-0x8F
    76  	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x90-0x9F
    77  	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xA0-0xAF
    78  	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xB0-0xBF
    79  	xx, xx, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xC0-0xCF
    80  	s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xD0-0xDF
    81  	s2, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s4, s3, s3, // 0xE0-0xEF
    82  	s5, s6, s6, s6, s7, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xF0-0xFF
    83  }
    84  
    85  // acceptRange gives the range of valid values for the second byte in a UTF-8
    86  // sequence.
    87  type acceptRange struct {
    88  	lo uint8 // lowest value for second byte.
    89  	hi uint8 // highest value for second byte.
    90  }
    91  
    92  var acceptRanges = [...]acceptRange{
    93  	0: {locb, hicb},
    94  	1: {0xA0, hicb},
    95  	2: {locb, 0x9F},
    96  	3: {0x90, hicb},
    97  	4: {locb, 0x8F},
    98  }
    99  
   100  // FullRune reports whether the bytes in p begin with a full UTF-8 encoding of a rune.
   101  // An invalid encoding is considered a full Rune since it will convert as a width-1 error rune.
   102  func FullRune(p []byte) bool {
   103  	n := len(p)
   104  	if n == 0 {
   105  		return false
   106  	}
   107  	x := first[p[0]]
   108  	if n >= int(x&7) {
   109  		return true // ASCII, invalid or valid.
   110  	}
   111  	// Must be short or invalid.
   112  	accept := acceptRanges[x>>4]
   113  	if n > 1 {
   114  		if c := p[1]; c < accept.lo || accept.hi < c {
   115  			return true
   116  		} else if n > 2 && (p[2] < locb || hicb < p[2]) {
   117  			return true
   118  		}
   119  	}
   120  	return false
   121  }
   122  
   123  // FullRuneInString is like FullRune but its input is a string.
   124  func FullRuneInString(s string) bool {
   125  	n := len(s)
   126  	if n == 0 {
   127  		return false
   128  	}
   129  	x := first[s[0]]
   130  	if n >= int(x&7) {
   131  		return true // ASCII, invalid, or valid.
   132  	}
   133  	// Must be short or invalid.
   134  	accept := acceptRanges[x>>4]
   135  	if n > 1 {
   136  		if c := s[1]; c < accept.lo || accept.hi < c {
   137  			return true
   138  		} else if n > 2 && (s[2] < locb || hicb < s[2]) {
   139  			return true
   140  		}
   141  	}
   142  	return false
   143  }
   144  
   145  // DecodeRune unpacks the first UTF-8 encoding in p and returns the rune and
   146  // its width in bytes. If p is empty it returns (RuneError, 0). Otherwise, if
   147  // the encoding is invalid, it returns (RuneError, 1). Both are impossible
   148  // results for correct, non-empty UTF-8.
   149  //
   150  // An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
   151  // out of range, or is not the shortest possible UTF-8 encoding for the
   152  // value. No other validation is performed.
   153  func DecodeRune(p []byte) (r rune, size int) {
   154  	n := len(p)
   155  	if n < 1 {
   156  		return RuneError, 0
   157  	}
   158  	p0 := p[0]
   159  	x := first[p0]
   160  	if x >= as {
   161  		// The following code simulates an additional check for x == xx and
   162  		// handling the ASCII and invalid cases accordingly. This mask-and-or
   163  		// approach prevents an additional branch.
   164  		mask := rune(x) << 31 >> 31 // Create 0x0000 or 0xFFFF.
   165  		return rune(p[0])&^mask | RuneError&mask, 1
   166  	}
   167  	sz := x & 7
   168  	accept := acceptRanges[x>>4]
   169  	if n < int(sz) {
   170  		return RuneError, 1
   171  	}
   172  	b1 := p[1]
   173  	if b1 < accept.lo || accept.hi < b1 {
   174  		return RuneError, 1
   175  	}
   176  	if sz == 2 {
   177  		return rune(p0&mask2)<<6 | rune(b1&maskx), 2
   178  	}
   179  	b2 := p[2]
   180  	if b2 < locb || hicb < b2 {
   181  		return RuneError, 1
   182  	}
   183  	if sz == 3 {
   184  		return rune(p0&mask3)<<12 | rune(b1&maskx)<<6 | rune(b2&maskx), 3
   185  	}
   186  	b3 := p[3]
   187  	if b3 < locb || hicb < b3 {
   188  		return RuneError, 1
   189  	}
   190  	return rune(p0&mask4)<<18 | rune(b1&maskx)<<12 | rune(b2&maskx)<<6 | rune(b3&maskx), 4
   191  }
   192  
   193  // DecodeRuneInString is like DecodeRune but its input is a string. If s is
   194  // empty it returns (RuneError, 0). Otherwise, if the encoding is invalid, it
   195  // returns (RuneError, 1). Both are impossible results for correct, non-empty
   196  // UTF-8.
   197  //
   198  // An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
   199  // out of range, or is not the shortest possible UTF-8 encoding for the
   200  // value. No other validation is performed.
   201  func DecodeRuneInString(s string) (r rune, size int) {
   202  	n := len(s)
   203  	if n < 1 {
   204  		return RuneError, 0
   205  	}
   206  	s0 := s[0]
   207  	x := first[s0]
   208  	if x >= as {
   209  		// The following code simulates an additional check for x == xx and
   210  		// handling the ASCII and invalid cases accordingly. This mask-and-or
   211  		// approach prevents an additional branch.
   212  		mask := rune(x) << 31 >> 31 // Create 0x0000 or 0xFFFF.
   213  		return rune(s[0])&^mask | RuneError&mask, 1
   214  	}
   215  	sz := x & 7
   216  	accept := acceptRanges[x>>4]
   217  	if n < int(sz) {
   218  		return RuneError, 1
   219  	}
   220  	s1 := s[1]
   221  	if s1 < accept.lo || accept.hi < s1 {
   222  		return RuneError, 1
   223  	}
   224  	if sz == 2 {
   225  		return rune(s0&mask2)<<6 | rune(s1&maskx), 2
   226  	}
   227  	s2 := s[2]
   228  	if s2 < locb || hicb < s2 {
   229  		return RuneError, 1
   230  	}
   231  	if sz == 3 {
   232  		return rune(s0&mask3)<<12 | rune(s1&maskx)<<6 | rune(s2&maskx), 3
   233  	}
   234  	s3 := s[3]
   235  	if s3 < locb || hicb < s3 {
   236  		return RuneError, 1
   237  	}
   238  	return rune(s0&mask4)<<18 | rune(s1&maskx)<<12 | rune(s2&maskx)<<6 | rune(s3&maskx), 4
   239  }
   240  
   241  // DecodeLastRune unpacks the last UTF-8 encoding in p and returns the rune and
   242  // its width in bytes. If p is empty it returns (RuneError, 0). Otherwise, if
   243  // the encoding is invalid, it returns (RuneError, 1). Both are impossible
   244  // results for correct, non-empty UTF-8.
   245  //
   246  // An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
   247  // out of range, or is not the shortest possible UTF-8 encoding for the
   248  // value. No other validation is performed.
   249  func DecodeLastRune(p []byte) (r rune, size int) {
   250  	end := len(p)
   251  	if end == 0 {
   252  		return RuneError, 0
   253  	}
   254  	start := end - 1
   255  	r = rune(p[start])
   256  	if r < RuneSelf {
   257  		return r, 1
   258  	}
   259  	// guard against O(n^2) behavior when traversing
   260  	// backwards through strings with long sequences of
   261  	// invalid UTF-8.
   262  	lim := end - UTFMax
   263  	if lim < 0 {
   264  		lim = 0
   265  	}
   266  	for start--; start >= lim; start-- {
   267  		if RuneStart(p[start]) {
   268  			break
   269  		}
   270  	}
   271  	if start < 0 {
   272  		start = 0
   273  	}
   274  	r, size = DecodeRune(p[start:end])
   275  	if start+size != end {
   276  		return RuneError, 1
   277  	}
   278  	return r, size
   279  }
   280  
   281  // DecodeLastRuneInString is like DecodeLastRune but its input is a string. If
   282  // s is empty it returns (RuneError, 0). Otherwise, if the encoding is invalid,
   283  // it returns (RuneError, 1). Both are impossible results for correct,
   284  // non-empty UTF-8.
   285  //
   286  // An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
   287  // out of range, or is not the shortest possible UTF-8 encoding for the
   288  // value. No other validation is performed.
   289  func DecodeLastRuneInString(s string) (r rune, size int) {
   290  	end := len(s)
   291  	if end == 0 {
   292  		return RuneError, 0
   293  	}
   294  	start := end - 1
   295  	r = rune(s[start])
   296  	if r < RuneSelf {
   297  		return r, 1
   298  	}
   299  	// guard against O(n^2) behavior when traversing
   300  	// backwards through strings with long sequences of
   301  	// invalid UTF-8.
   302  	lim := end - UTFMax
   303  	if lim < 0 {
   304  		lim = 0
   305  	}
   306  	for start--; start >= lim; start-- {
   307  		if RuneStart(s[start]) {
   308  			break
   309  		}
   310  	}
   311  	if start < 0 {
   312  		start = 0
   313  	}
   314  	r, size = DecodeRuneInString(s[start:end])
   315  	if start+size != end {
   316  		return RuneError, 1
   317  	}
   318  	return r, size
   319  }
   320  
   321  // RuneLen returns the number of bytes required to encode the rune.
   322  // It returns -1 if the rune is not a valid value to encode in UTF-8.
   323  func RuneLen(r rune) int {
   324  	switch {
   325  	case r < 0:
   326  		return -1
   327  	case r <= rune1Max:
   328  		return 1
   329  	case r <= rune2Max:
   330  		return 2
   331  	case surrogateMin <= r && r <= surrogateMax:
   332  		return -1
   333  	case r <= rune3Max:
   334  		return 3
   335  	case r <= MaxRune:
   336  		return 4
   337  	}
   338  	return -1
   339  }
   340  
   341  // EncodeRune writes into p (which must be large enough) the UTF-8 encoding of the rune.
   342  // It returns the number of bytes written.
   343  func EncodeRune(p []byte, r rune) int {
   344  	// Negative values are erroneous.  Making it unsigned addresses the problem.
   345  	switch i := uint32(r); {
   346  	case i <= rune1Max:
   347  		p[0] = byte(r)
   348  		return 1
   349  	case i <= rune2Max:
   350  		p[0] = t2 | byte(r>>6)
   351  		p[1] = tx | byte(r)&maskx
   352  		return 2
   353  	case i > MaxRune, surrogateMin <= i && i <= surrogateMax:
   354  		r = RuneError
   355  		fallthrough
   356  	case i <= rune3Max:
   357  		p[0] = t3 | byte(r>>12)
   358  		p[1] = tx | byte(r>>6)&maskx
   359  		p[2] = tx | byte(r)&maskx
   360  		return 3
   361  	default:
   362  		p[0] = t4 | byte(r>>18)
   363  		p[1] = tx | byte(r>>12)&maskx
   364  		p[2] = tx | byte(r>>6)&maskx
   365  		p[3] = tx | byte(r)&maskx
   366  		return 4
   367  	}
   368  }
   369  
   370  // RuneCount returns the number of runes in p.  Erroneous and short
   371  // encodings are treated as single runes of width 1 byte.
   372  func RuneCount(p []byte) int {
   373  	np := len(p)
   374  	var n int
   375  	for i := 0; i < np; {
   376  		n++
   377  		c := p[i]
   378  		if c < RuneSelf {
   379  			// ASCII fast path
   380  			i++
   381  			continue
   382  		}
   383  		x := first[c]
   384  		if x == xx {
   385  			i++ // invalid.
   386  			continue
   387  		}
   388  		size := int(x & 7)
   389  		if i+size > np {
   390  			i++ // Short or invalid.
   391  			continue
   392  		}
   393  		accept := acceptRanges[x>>4]
   394  		if c := p[i+1]; c < accept.lo || accept.hi < c {
   395  			size = 1
   396  		} else if size == 2 {
   397  		} else if c := p[i+2]; c < locb || hicb < c {
   398  			size = 1
   399  		} else if size == 3 {
   400  		} else if c := p[i+3]; c < locb || hicb < c {
   401  			size = 1
   402  		}
   403  		i += size
   404  	}
   405  	return n
   406  }
   407  
   408  // RuneCountInString is like RuneCount but its input is a string.
   409  func RuneCountInString(s string) (n int) {
   410  	ns := len(s)
   411  	for i := 0; i < ns; n++ {
   412  		c := s[i]
   413  		if c < RuneSelf {
   414  			// ASCII fast path
   415  			i++
   416  			continue
   417  		}
   418  		x := first[c]
   419  		if x == xx {
   420  			i++ // invalid.
   421  			continue
   422  		}
   423  		size := int(x & 7)
   424  		if i+size > ns {
   425  			i++ // Short or invalid.
   426  			continue
   427  		}
   428  		accept := acceptRanges[x>>4]
   429  		if c := s[i+1]; c < accept.lo || accept.hi < c {
   430  			size = 1
   431  		} else if size == 2 {
   432  		} else if c := s[i+2]; c < locb || hicb < c {
   433  			size = 1
   434  		} else if size == 3 {
   435  		} else if c := s[i+3]; c < locb || hicb < c {
   436  			size = 1
   437  		}
   438  		i += size
   439  	}
   440  	return n
   441  }
   442  
   443  // RuneStart reports whether the byte could be the first byte of an encoded,
   444  // possibly invalid rune.  Second and subsequent bytes always have the top two
   445  // bits set to 10.
   446  func RuneStart(b byte) bool { return b&0xC0 != 0x80 }
   447  
   448  // Valid reports whether p consists entirely of valid UTF-8-encoded runes.
   449  func Valid(p []byte) bool {
   450  	n := len(p)
   451  	for i := 0; i < n; {
   452  		pi := p[i]
   453  		if pi < RuneSelf {
   454  			i++
   455  			continue
   456  		}
   457  		x := first[pi]
   458  		if x == xx {
   459  			return false // Illegal starter byte.
   460  		}
   461  		size := int(x & 7)
   462  		if i+size > n {
   463  			return false // Short or invalid.
   464  		}
   465  		accept := acceptRanges[x>>4]
   466  		if c := p[i+1]; c < accept.lo || accept.hi < c {
   467  			return false
   468  		} else if size == 2 {
   469  		} else if c := p[i+2]; c < locb || hicb < c {
   470  			return false
   471  		} else if size == 3 {
   472  		} else if c := p[i+3]; c < locb || hicb < c {
   473  			return false
   474  		}
   475  		i += size
   476  	}
   477  	return true
   478  }
   479  
   480  // ValidString reports whether s consists entirely of valid UTF-8-encoded runes.
   481  func ValidString(s string) bool {
   482  	n := len(s)
   483  	for i := 0; i < n; {
   484  		si := s[i]
   485  		if si < RuneSelf {
   486  			i++
   487  			continue
   488  		}
   489  		x := first[si]
   490  		if x == xx {
   491  			return false // Illegal starter byte.
   492  		}
   493  		size := int(x & 7)
   494  		if i+size > n {
   495  			return false // Short or invalid.
   496  		}
   497  		accept := acceptRanges[x>>4]
   498  		if c := s[i+1]; c < accept.lo || accept.hi < c {
   499  			return false
   500  		} else if size == 2 {
   501  		} else if c := s[i+2]; c < locb || hicb < c {
   502  			return false
   503  		} else if size == 3 {
   504  		} else if c := s[i+3]; c < locb || hicb < c {
   505  			return false
   506  		}
   507  		i += size
   508  	}
   509  	return true
   510  }
   511  
   512  // ValidRune reports whether r can be legally encoded as UTF-8.
   513  // Code points that are out of range or a surrogate half are illegal.
   514  func ValidRune(r rune) bool {
   515  	switch {
   516  	case r < 0:
   517  		return false
   518  	case surrogateMin <= r && r <= surrogateMax:
   519  		return false
   520  	case r > MaxRune:
   521  		return false
   522  	}
   523  	return true
   524  }